W ` an uutttuuut bebe fo q s?? oorr thhe ffish thhat live inn oour

We’ve all heard about how gardening of all types can
be a great stress-buster for us humans, but what about
for the fish that live in our aquaponic systems?
170
Maximum Yield USA | July 2013
AQUAPONIC STRESS FACTORS
Aquaponic gardening is a fascinating way to grow
two food products—vegetables and fish—together
in an organic, symbiotic ecosystem. And while growes is a familiar process for most of us,
ing vegetables
me fish for food is unfamiliar to many
growing game
gardeners and can be a somewhat intimidating
en for experienced aquarium hobbyists,
activity. Even
ate-sized tilapia is a whole differr
growing a plate-sized
ent animal. The key to growing fish for
ny fish, for that matter) in
food (or any
aquaponics is to consider what
stresses the fish experience
in a captive environment
sening
and then lessening
ng
or eliminating
e are
them. There
ries
three categories
s:
of fish stress:
emical
physical, chemical
al.
and biological.
PHYSICAL STRESS
Tilapia thrive in densly populated conditions.
Physical stress
ess includes all the environmental
hat we control for our fish, the most
conditions that
important of which is temperature. All fish have a
temperature range within which they will thrive,
and a wider range within which they will survive.
Fish are cold-blooded animals; thus, they do not
have the ability to expend energy to maintain a constant internal body temperature like we do. They
are completely at the mercy of the temperature of
their surrounding water. If that water temperature
goes outside of their optimal (or, thriving) range,
fish will eat less, or stop eating all together, and
they become more susceptible to disease. That said,
this is sometimes carefully employed as a technique
“WHILE GROWING VEGETABLES IS
A FAMILIAR PROCESS FOR MOST OF
US, GROWING GAME FISH FOR FOOD
IS UNFAMILIAR TO MANY GARDENERS
AND CAN BE A SOMEWHAT
INTIMIDATING ACTIVITY.”
called cold banking to slow down their growth rate.
Cold banking is especially effective with fingerlings
when you are trying to stagger your fish production.
Another form of physical stress is sudden exposure
to light and vibration. Fish are alarmed when we
flip on a light switch and take their world instantly
172
Maximum Yield USA | July 2013
AQUAPONIC STRESS FACTORS
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from night to day. They will sometimes even bang
against the walls of their tank to escape the light.
However, just like with cold banking, this sensitivity to light can be used to the aquaculturalist’s
advantage by employing a technique called phase
shifting, whereby you trick the fish into thinking
that it is spawning
ing season (or not) by timing the
amount of lightt they get during the day to mimic
the season in which they normally spawn (or not).
And because they “hear” vibrations with their
entire bodies, rapping against the wall of a tank
ng to them and will also
feels like yelling
ndue stress.
cause them undue
Interestingly, another form of
physical stress can be water
riginating
velocity. Fish originating
from still lake waters,
such as tilapia and
perch, do not like
ent
much movement
in their tank water.
However, river fish like
trout find it stressful
essful not to
have a current present in their tank.
“IF THAT
HAT WATER TEMPERATURE
GOES OUTSIDE OF THEIR OPTIMAL
(OR, THRIVING) RANGE, FISH WILL
EAT LESS, OR STOP EATING ALL
TOGETHER, AND THEY BECOME
MORE SUSCEPTIBLE TO DISEASE.”
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Maximum Yield USA | July 2013
AQUAPONIC STRESS FACTORS
CHEMICAL STRESS
Chemical stress is mostly centered on maintaining the quality of the water. Escalating ammonia
and nitrite levels stress our fish. This can easily
happen at the beginning of an aquaponic system’s
life if the fish are introduced to the system before
the nitrifying bacteria have been fully established
(A.K.A fully cycled). If you see ammonia levels
approaching 8 ppm or nitrite levels approaching
“IF YOU SEE YOUR pH DROPPING TO
6.4 OR BELOW, YOU WILL WANT TO
TAKE IMMEDIATE ACTION TO BUFFER
IT BACK UP USING A CALCIUM OR
POTASSIUM COMPOUND.”
1 ppm, you should do a one-third water change to
dilute the level of unconverted toxic waste matter
in your tank and allow the bacteria to catch up.
Once you are fully cycled, the most common
reason for a spike in ammonia and nitrite levels in
an established system is that something is decaying somewhere in your system. Usually, this is an
indication of a dead fish. While dead fish usually
float to the surface and are easily detected, this
isn’t always true and a rotting fish carcass can very
quickly spike your ammonia and endanger the
rest of your fish. The next most common reason is
that there is an anaerobic zone somewhere in your
grow beds. This describes an area of your beds
where material has built up and is not decomposing aerobically, i.e. with oxygen, but has instead
become stagnant. It probably also smells badly, and
typically nothing will grow there. Anaerobic zones
are easily remedied by simply agitating the media
with a stick and allowing the stuck, rotting material
to wash out of the grow bed.
Tilapia are ideal aquaponics candidates.
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Maximum Yield USA | July 2013
AQUAPONIC STRESS FACTORS
Note that in contrast to ammonia and nitrite,
nitrate levels can go as high as 500 to 700 ppm
without harming the fish.
Maintaining a very low pH (below 6.0) can also
be stressful. If you see your pH dropping to 6.4
or below, you will want to take immediate action
to buffer it back up using a calcium or potassium
compound. Finally, insufficient filtration of the
solid waste and not enough dissolved oxygen
(less than 4 ppm) are, not surprisingly, other
forms of chemical stress.
BIOLOGICAL STRESS
Aquaponic set-ups are designed to grow two food products—
vegetables and fish—together in a symbiotic ecosystem.
This last category refers to viruses, bacteria, fungi
and parasites. Just like in our world, most of
these pathogens are often present but only fully
express themselves when the right conditions
occur. For fish, this likely means that some of the
stress factors listed above must also be in place
for biological threats to have an impact.
In aquaponics we have adopted the technique
of salting fish—that is, adding salt (sodium chloride) to the water to help them ward off disease.
But this practice can be harmful to our plants
because they may be sensitive to sodium. Also,
I’ve recently heard that it is the chlorine, not the
sodium, which helps the fish. So, you can actually
get the same effect with a more plant-friendly
treatment such as potassium chloride or magnesium chloride.
So, just think like a fish and give them a relatively stress-free environment and they will live
long in your aquaponics system—and be delicious at harvest!
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Maximum Yield USA | July 2013